Cancer continues to be one of the foremost health problems. Conventional treatments such as surgery and chemotherapy have been extremely successful in certain cases; in other instances, much less so. Radiation therapy has also exhibited favorable results in many cases, while failing to be completely satisfactory and effective in all instances. An alternative form of radiation therapy, known as microbeam radiation therapy (MRT) may be used to treat certain tumors for which the conventional methods have been ineffective.
MRT differs from conventional radiation therapy by employing multiple parallel fan beams of radiation with a narrow dimension or thickness that may be on the order of 10 um to 200 um. The thickness of the microbeams is dependent upon the capacity of tissue surrounding a beam path to support the recovery of the tissue injured by the beam. It has been found that certain types of cells, notably endothelial cells lining blood vessels, have the capacity to migrate over microscopic distances, infiltrating tissue damaged by radiation and reducing tissue necrosis in the beam path. In MRT, sufficient unirradiated or minimally irradiated microscopic zones remain in the normal tissue, through which the microbeams pass, to allow efficient repair of irradiation-damaged tissue. As a result, MRT is fundamentally different from other forms of radiation therapy.
In conventional forms of radiation therapy, including the radiosurgical techniques employing multiple convergent beams of gamma radiation, each beam is at least several millimeters in diameter, so that the biological advantage of rapid repair by migrating or proliferating endothelial cells is minimal or nonexistent. Observations of the regeneration of blood vessels following MRT indicate that endothelial cells cannot efficiently regenerate damaged blood vessels over distances on the order of thousands of micrometers (μm). Thus, in view of this knowledge concerning radiation pathology of normal blood vessels, the skilled artisan may select a microbeam thickness as small as 10 μm to 200 μm. Further, the microbeams may include substantially parallel, non-overlapping, planar beams with center-to-center spacing of from about 50 μm to about 500 μm. Also, the beam energies may range from about 30 to several hundred keV. These microbeams result in a dosage profile with peaks and valleys. The radiation dosage in the peaks is large enough to kill the targeted tumor, but also kills healthy cells in the peak dosage areas. The radiation dosage in the valleys is small enough to prevent any damage to cells in the valley dosage areas.
A division of a radiation beam into microbeams and the use of a patient exposure plan that provides non-overlapping beams in the tissue surrounding the target tumor allows the non-target tissue to recover from the radiation injury by migration of regenerating endothelial cells of the small blood vessels to the areas in which the endothelial cells have been injured beyond recovery. Therefore, the probability of radiation-induced coagulative necrosis in normal, non-targeted tissue is lowered, which may improve the effectiveness of clinical radiation therapy for deep-seated tumors. The use of microbeams may be of special benefit for deep tumors.
Various studies have shown the microbeam tissue-sparing effect for X-ray microbeams. Although other methods and processes are known for radiation therapy, none provides a method for performing radiation therapy while avoiding significant radiation-induced damage to tissues surrounding the target.
Present radiation therapies often take many days and weeks of treatment to provide enough radiation to a target tumor. On the other hand, MRT can provide an effectual treatment in single visit. Very high energy radiation may be used with MRT that results in the destruction of tumor tissue while allowing for the regeneration of healthy tissue affected by the microbeam fan beams.
Further, MRT provides a method for treating cancerous tumors by using extremely small radiation microbeams increasing the precision and accuracy of radiation therapy. MRT also provides a method of using extremely small microbeams of radiation to unexpectedly produce effective radiation therapy while avoiding significant radiation-induced damage to non-target tissues.
A major benefit of MRT is that the microbeams are so narrow that the vasculature of the tissue through which the microbeams pass can repair itself by the infiltration of endothelial cells from surrounding unirradiated tissue. Present knowledge indicates that such infiltration can take place only over distances on the order of less than 500 μm depending on the tissue being irradiated. The dimensions of the microbeams and the configuration of the microbeam array are therefore determinable with reference to the susceptibility of the target tissue and the surrounding tissue to irradiation and the capacities of the various involved tissues to regenerate.
U.S. Pat. No. 5,339,247 to Slatkin et al. entitled Method for Microbeam Radiation Therapy provides background related to MRT, and is hereby incorporated by reference for all purposes.